Fix config file use and options
Fix config file use and options

Now the default config file is optional.

Also adds the ability to ignore the config file entirely with `--config none`.

jonboulle/github-issues-import,nrc/github-issues-import,LalatenduMohanty/github-issues-import,crawford/github-issues-import,abrkn/github-issues-import,danmichaelo/github-issues-import,simonfork/github-issues-import,IQAndreas/github-issues-import,lukesmith/github-issues-import